Becoming Oldest-Old: Evidence from Historical U.S. Data

We argue that the environment determines life span, using historical data to show that such indicators of environmental insults in early childhood and young adulthood as quarter of birth, residence, occupation, wealth, and the incidence of specific infectious diseases affected older age mortality. Consistent with improvements in early life factors, we find that the effect of quarter of birth on older age mortality has diminished over the twentieth century and that the declining impact of quarter of birth explains 16 to 17 percent of the difference in ten year mortality rates of Americans age 60-79 in 1900 and in 1960-1980. We estimate that at least one-fifth of the increase between 1900 and 1999 in the probability of a 65 year old surviving to age 85 may be attributable to early life conditions. We also present suggestive evidence on the mortality trajectory of the oldest old in the first half of the twentieth century that implies that the shape of the mortality trajectory, though not its level, has remained constant.